program P5_4;
var n:integer;
    i,j,k:integer;
    i_s, o_s:string[100];
    dusage:array[0..9] of byte;
    c:char;
    odds:shortint;
    ps:integer;
begin
write('>>> enter N: ');
readln(n);
writeln('>>> now enter numbers [ <= N]:');
readln(i_s);
if length(i_s) > n then delete(i_s, length(i_s)+1, length(i_s)-n+1);
for i:=1 to n do begin
	inc( dusage[ord(i_s[i])-ord('0')] );
	end;
for i:=9 downto 0 do begin
	if odd(dusage[i]) then
		begin
		inc(odds);
		ps:=i;
		end
	else
		for j:=1 to (dusage[i] div 2) do
			insert( chr( i+ord('0') ), o_s, length(o_s)+1);
	end;
j:=length(o_s);
if odds>1 then
	writeln('not possible')
else
	begin
	if odds=1 then insert( chr(ps+ord('0')), o_s, j+1);
	for i:=j downto 1 do
		begin
		insert(o_s[i], o_s, length(o_s)+1);
		end;
	end;
writeln(o_s);
end.
